Various types of prior art lighting structures will be described that generally describe a set of LEDs and a set of lenses. The LEDs and lenses are translatable relative to each other to steer a beam of light or to otherwise customize the emission.
Directional lighting is important in many contexts, for example in providing illumination for task areas in a workplace, for highlighting objects in a retail space or an artistic exhibition, for illuminating walkways and roadways outdoors, and many more applications. Commonly-used light fixtures that provide the option to adjust lighting directionality typically include an illumination “head” that can be swiveled to point in a desired direction. Multiple heads are often included in a single light bank or in a configurable system such as a track lighting system. Adjustments to the angular spread of the output beam from each head is typically achieved by installing a bulb with the desired output beam width.
A planar adjustable luminaire design is disclosed in Joseph Ford's PCT/US2014/057873, entitled “Microstructured Waveguide Illuminator,” and William M. Mellette, Glenn M. Schuster, and Joseph E. Ford's paper entitled, “Planar waveguide LED illuminator with controlled directionality and divergence,” Optics Express vol. 22 No. S3, 2014. This design offers the advantage of a compact low-profile form factor with wide adjustability. The luminaire uses an edge-illuminated lightguide with periodic extraction features that is mated to an array of lenses or reflectors (“focusing elements”). By adjusting the relative location of the extraction features and the focusing elements, the direction of the beam can be steered and the angular width of the output beam can be adjusted.
FIG. 1 is an exploded view of such a design. It includes a lightguide 10 that is edge-lit by a light source 11, in this example composed of light emitting diodes (LEDs) 17 and associated coupler optics 18. The lightguide 10 may be of a continuous-mode type as shown in FIG. 1 or a stepped-mode type. In either case, the lightguide 10 includes a periodic array of extraction features 12. These features 12 reflect or scatter light so that it is no longer trapped in guided modes of the lightguide 10 and instead exits the lightguide 10 to interact with the array 14 of focusing elements 15. The extraction features 12 shown in FIG. 1 are reflective and are preferably shaped as prisms to deflect guided light toward the focusing elements 15, but may also be shaped as cones, hemispheres, or other shapes. They lie approximately in the focal plane of the focusing elements 15 so that light scattered by the extraction elements 12 is substantially collimated by the focusing elements 15. The focusing elements 15 are all in a single plane in the array 14. The focusing elements 15 may be refractive lenses that transmit the substantially collimated light, or may be curved reflectors that reflect back collimated light so that it transits through the lightguide 10 before exiting the luminaire into the environment.
FIG. 2 is a cross-section view of a portion of the adjustable luminaire of FIG. 1, showing the array 14 composed of dielectric-filled reflective focusing elements 15 with a reflective coating 19, and two associated extraction features 12. Light from the light source 11 is guided in the lightguide 10. Some of the light is deflected by extraction features 12 to exit the lightguide 10 and enter the focusing element array 14. These light rays 13 reflect off the reflective coating 19, becoming partially collimated, and then transit through the lightguide 10 before exiting the luminaire as the steered output light beam 16. The light rays emanating from the light source 11 and traveling within the lightguide 10 are not depicted in FIG. 2 in the interest of visual clarity; only the example light rays 13 reflected by one of the focusing elements 15 are shown.
Each individual focusing element 15 serves to substantially collimate the light reflected or scattered by the corresponding extraction feature 12 so that it is emitted into the environment as a directional beam 16 of narrow angular width. Control over the directionality of the individual beams 16 is achieved by varying the relative location of the extraction feature 12 and the focusing element 15. This can be achieved by translating the array 14 of focusing elements 15 relative to the extraction features 12 in the lightguide 10. As the location of the extraction feature 12 moves from the center of the focusing element 15 to the edge, the output beam 16 is steered from perpendicular to the plane of the lightguide 10 to a high angle.
If all focusing elements 15 in the array 14 bear the same orientation relative to their corresponding extraction features 12, then all the output beams 16 will point in the same direction. In that case, all the focusing elements are contributing to a narrow aggregate beam pointed in a single direction. Alternatively, if the focusing elements 15 in the array 14 are twisted relative to the array of extraction features 12, then each of the output beams 16 will point in a somewhat different direction. In that case, the output aggregate beam is the sum of the differently-pointed beams and results in a wider aggregate beam. Therefore, independent control over beam pointing and aggregate beam width is provided by translating and twisting the relative position of the focusing element array 14 and the extraction element array.
The prior art describes several implementations of this design, including the use of motorized actuators and a control system to provide remote control over the output characteristics of the adjustable luminaire. The prior art also describes the use of a switchable material in the lightguide that provides for pixelated control over the location and presence of the extraction features. The prior art describes a mechanism for controlling this whereby a layer of liquid crystal material with electrically-adjustable refractive index is placed on the face of the lightguide. In its low-refractive-index state, this material acts as cladding to keep light confined within the lightguide. Pixelated electrodes allow it to be locally switched to a high-refractive-index state, allowing light to locally interact with a tilted mirror array and be ejected from the lightguide. This provides a mechanism for local control over the location of the extraction feature. The design can be implemented with a stationary lens array to provide a steerable luminaire design with no moving parts.
FIG. 3 depicts a luminaire design that includes an array of light emitters 30, each coupled to a focusing element 31 (in this case, reflective focusing elements). The focusing elements 31 are depicted as transparent so as to view the light emitters 30. The light emitters 30 are shown below the focusing elements 31, and the reflected light is directed back towards the light emitters 30. No lightguide is needed. The light emitters 30 may be of any type, but are preferably LEDs or laser diodes for compactness and efficiency. Vertical-cavity surface-emitting laser diodes (VCSELs) are another option for the light emitters 30. In all cases, the light emitters 30 are connected in a network electrically and supported by metal heat spreading supporting structures 32. The electrical connections bring electrical power to the light emitters 30 to drive them, and the heat spreading supporting structures 32 are used to route heat away from the emitters 30 to reduce operating temperature. The electrical connections and heat spreading supporting structures 32 may be optionally combined into a single structure or even combined into a single element. This is shown in the example system of FIG. 3, where a strip of metal-core printed circuit board (MCPCB) (forming the heat spreading support structures 32) connects individual light emitters 30 in a line, providing both electrical connections and a heat spreading element.
It is advantageous to design the system so that the emitting area of the light emitter 30 is much smaller than the area of the focusing element 31, enabling the focusing element 31 to produce a beam of a narrow angular width. For example, the diameter of the focusing element 31 may be approximately 5 to 20 times the diameter of the light emitting area of the emitter 30.
When implemented with a reflective focusing element array 34 (an array of concave mirrors), it is also advantageous to minimize the area of the electrical connections and heat-spreading support structures 32, as these will shadow the reflected light and reduce system optical efficiency. In FIG. 3, the heat spreading support structures 32 span the entire width of each focusing element 15, so the resulting aggregate shadow may be significant and can create a perceived artifact on an illuminated object.
The direct-lit design uses the arrayed light emitters 30 in place of a lightguide and extraction features used in the edge-lit designs. It shares the same adjustable functionality, however. Aggregate beam steering is achieved by translating the array of focusing elements 31 relative to the array of light emitters 30, and aggregate beam broadening can be achieved by twisting the array of focusing elements 31 relative to the array of light emitters 30.
An advantage of the direct-lit design is that it can be implemented with high optical efficiency in a small form factor. In contrast, the edge-lit design requires a row of LEDs of a length needed to generate all the required light within the lightguide.
While the prior art described above provides for major advantages compared to conventional steerable luminaires, it still suffers from various limitations affecting implementation for specific applications. These include: i) reduced optical efficiency and non-uniform aggregate beam due to shadowing from electrical connections and heat-spreading elements; ii) limited flexibility to adjust aggregate beam shape; and iii) loss of optical efficiency due to cross-talk during beam steering.